Steel wire rod having lubricating coating film that has excellent corrosion resistance and workability

ABSTRACT

The present invention provides a steel wire rod including a lubricating coating film, which can reconcile workabilities such as wire drawability, spike property, ball ironing property and film removability, and corrosion resistance such as long-term rust prevention property. The steel wire rod includes a lubricating coating film on a surface, wherein the lubricating coating film contains a water-soluble silicate and a water-soluble tungstate, a mass ratio of water-soluble tungstate/water-soluble silicate being in a range of 0.7 to 10, and contains no phosphorus

TECHNICAL FIELD

The present invention relates to a steel wire rod having a lubricating coating film containing no phosphorus on a surface.

BACKGROUND ART

In plastic working of a steel wire and a steel wire rod, since friction generated when surfaces of metals (particularly a die and a workpiece) are violently rubbed against each other may cause an increase in working energy, heat generation, seizure phenomenon, and the like, there have been used various lubricants which aim to reduce a friction force. Oils, soaps, and the like have been used as the lubricant for a long time, and the friction force has been reduced by supplying them to a friction surface to form a fluid lubricating coating film. In plastic working in which sliding occurs under high surface pressure involving significant heat generation due to an increase in surface area, a seizure phenomenon is likely to generate due to shortage of lubrication, lubricating coating film disruption, and the like. Therefore, there has been popularized technology in which a surface of a metal material is coated in advance with a solid coating film, for example, an inorganic coating film such as a borate coating film or a phosphate crystal coating film, which has sufficient coating film strength and exists at an interface between a die and a workpiece and is therefore less likely to cause lubricating coating film disruption even under high surface pressure, thus making it possible to avoid direct contact between metals. In particular, a composite coating film composed of a zinc phosphate coating film and a soap layer (hereinafter sometimes referred to as a chemical conversion coating film) has widely been employed because of having high workability and corrosion resistance.

In recent years, there have been surging a wide range of requirements for a solid coating film, for example, further reduction in working energy and increase in working degree, coping with a hard-to-work material, environmental protection of a coating film process (for example, a phosphatizing treatment has an environmental conservation problem because of generation of numerous industrial wastes such as sludge), taking measures to phosphorizing of a bolt (if phosphorus in a coating film component remains during a heat treatment after heading of a high strength bolt, phosphorus enters into a steel, thus causing brittle fracture), and the like. While global environment conservation is taken into consideration to these requirements, a solid coating film having high lubricity has been developing. This technology enables formation of a coating film having high lubricity by a simple step of only applying an aqueous plastic working lubricant to a surface of a workpiece, followed by drying.

Patent Document 1 discloses an aqueous lubricating coating agent for plastic working of a metal material, which is a composition comprising an aqueous inorganic salt (A) and a wax (B) dissolved or dispersed in water, wherein a solid component weight ratio (B)/(A) is in a range of 0.3 to 1.5; and a coating film forming method thereof.

Patent Document 2 discloses an aqueous lubricating coating agent for plastic working of a metal material, comprising an alkali metal borate (A), wherein the alkali metal borate (A) contains lithium borate, a molar ratio of lithium to the entire alkali metal in the alkali metal borate (A) is in a range of 0.1 to 1.0, and also a molar ratio (B/M) of boric acid B to an alkali metal M of the alkali metal borate (A) is in a range of 1.5 to 4.0; and a coating film forming method thereof. It is considered that this technology suppresses crystallization of a coating film caused by moisture absorption of the coating film, thus enabling formation of a coating film having not only workability but also high corrosion resistance.

Patent Document 3 discloses a water-soluble lubricant for non-phosphorus based plastic working, comprising an inorganic solid lubricant as a component A, a wax as a component B, and a water-soluble inorganic metal salt as a component C, wherein a solid component mass ratio of the component A to the component B (component A/component B) is in a range of 0.1 to 5, and a solid component mass ratio of the component C to the total amount of the component A, the component B, and the component C (component C/(component A+component B+component C)) is in a range of 1 to 30°. It is considered that this technology is directed to a lubricant containing no phosphorus and enables realization of corrosion resistance equal to that of a chemical conversion coating film.

Patent Document 4 discloses an aqueous lubricating coating agent comprising an aqueous inorganic salt (A), at least one lubricant (B) selected from molybdenum disulfide and graphite, and a wax (C), these components being dissolved or dispersed in water, wherein (B)/(A) is in a range of 1.0 to 5.0 in terms of a solid component weight ratio, and (C)/(A) is in a range of 0.1 to 1.0 in terms of a solid component weight ratio; and a coating film forming method thereof. It is considered that this technology enables realization of high workability having the same level as that of a chemical conversion coating film by mixing a conventional aqueous lubricating coating agent with molybdenum disulfide or graphite.

Patent Document 5 discloses a coating film forming agent comprising a silicate (A), a polycarboxylate (B), a hydrophilic polymer and/or a hydrophilic organic lamellar structure (C), and a molybdate and/or a tungstate (D), a mass ratio of each component being a predetermined ratio.

As mentioned in Patent Documents 1 to 5, the aqueous inorganic salt is an essential component in the solid coating film of the aqueous lubricating coating agent. The reason is that the lubricating coating film composed of the aqueous inorganic salt has sufficient coating film strength and, as mentioned above, the lubricating coating film exists at an interface between a die and a workpiece and is therefore less likely to cause lubricating coating film disruption even under high surface pressure, thus making it possible to avoid direct contact between metals. Therefore, in the aqueous lubricating coating agent, it is possible to maintain a satisfactory lubricated state during plastic working by using a solid coating film composed of an aqueous inorganic salt or a water-soluble resin in combination with an appropriate lubricant capable of reducing a friction coefficient.

A description will be made of coating film formation mechanism of the aqueous lubricating coating agent composed of a water-soluble component. An aqueous inorganic salt of a water-soluble component is in a state of being dissolved in water in a lubricating treatment solution and, when a lubricant is applied on a surface of a metal material and then dried, water as a solvent is vaporized to form a lubricating coating film. In that case, the aqueous inorganic salt is precipitated as a solid substance on the surface of the metal material to form a solid coating film. The solid coating film thus formed has a coating film strength capable of enduring plastic working, and exhibits satisfactory lubricity during plastic working by mixing with an appropriate lubricant capable of reducing a friction coefficient.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: WO 02/012420 A

Patent Document 2: JP 2011-246684 A

Patent Document 3: JP 2013-209625 A

Patent Document 4: WO 02/012419 A

Patent Document 5: JP 2002-363593 A

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, in the lubricating coating films of Patent Documents 1 to 5, rust prevention property over a long term of two or more months is drastically inferior as compared with the above-mentioned chemical conversion coating films, thus failing to enhance to a practical level. This is because a main component of the coating film is a water-soluble component and therefore easily absorbs or transmits moisture ip the atmosphere, leading to easy contact between a steel material and moisture. In Patent Document 2, corrosion resistance is improved by suppressing crystallization of the coating film due to moisture absorption, however, moisture absorption itself is not suppressed, thus failing to obtain sufficient corrosion resistance. It was mentioned that the aqueous lubricating coating film mentioned in Patent Document 3 exhibited corrosion resistance, which is equal to or better than that of the chemical conversion coating film, in a corrosion resistance test in a laboratory in which rusting is accelerated using a thermo-hygrostat. Commonly, the lubricating coating film is actually used in the environment where dusts and powders, and mists of a picking agent are adhesible. In such severe environment, corrosion resistance is actually inferior as compared with the chemical conversion coating film. As mentioned above, there has never been an aqueous lubricating coating film containing no phosphorus, having rust prevention property which is equal to or better than that of the chemical conversion coating film.

Examples of the aqueous inorganic salt capable of obtaining comparatively high corrosion resistance include an alkali metal salt of a silicate (hereinafter sometimes referred to as a silicate) and an alkali metal salt and/or an ammonium salt of a tungstate (hereinafter sometimes referred to as a tungstate). These aqueous inorganic salts are also mentioned in Patent Document 1, Patent Document 4, and Patent Document 5. However, they are far inferior in practical corrosion resistance as compared with the chemical conversion coating film.

The water-soluble silicate has a property that is less likely to transmit moisture among the water-soluble aqueous inorganic salts and also has very high adhesion to a material. Because of this property, it is a material that can exhibit comparatively high corrosion resistance, but not as much as the chemical conversion coating film. This is because the water-soluble silicate is crosslinked to from a network structure in a coating film formation process in which water as a solvent of a lubricant is vaporized. However, because of this network structure, the coating film of the water-soluble silicate is too brittle as a lubricating coating film. Therefore, when a base material is worked, it is sometimes impossible to sufficiently conform because of cracks of the coating film. Too high adhesion due to the network structure may cause insufficient film removal, thus resulting in various defects in the subsequent step. For example, when plating is performed in the subsequent step, inclusion of a coating film component may cause not only contamination of a plating solution, but also poor plating in the portion where the coating film component remains.

The water-soluble tungstate is less likely to absorb moisture from external air when a coating film is formed. This is because granular crystals are formed when the water-soluble tungstate forms a coating film. Further, the water-soluble tungstate has a property that forms a passive coating film having a self-repair function on a surface of a steel material, and use of the water-soluble tungstate as the coating film component enables expectation of formation of a coating film having high corrosion resistance. Because of its high water solubility, it is possible to easily perform film removal with an aqueous solution. However, the water-soluble tungstate is crystalline and is therefore inferior in adhesion to a material and cannot form a uniform coating film, thus failing to obtain corrosion resistance and workability as expected. For example, it is possible to enhance adhesion and uniformity of a coating film by adding a synthetic resin component in a lubricant, but the corrosion resistance is drastically inferior as compared with a chemical conversion coating film.

Both of the aqueous lubricating coating agents containing an aqueous water-soluble inorganic salt mentioned in Patent Documents 1 to 3 were inferior in workability as compared with a chemical conversion coating film. This tendency is particularly notable in severe working wherein a surface area expansion ratio becomes at least several tens of times (hereinafter sometimes referred to as severe working), thus causing insufficient deformation of a material, decrease in die life, occurrence of seizure, and the like.

In the aqueous lubricating coating agent mentioned in Patent Document 4, it is possible to obtain workability, which is equal to or better than that of a chemical conversion coating film, even during severe working by inclusion of molybdenum disulfide and graphite. However, inclusion of these components colors a lubricating liquid black, leading to extreme contamination of an apparatus and peripheral parts, and operators. Molybdenum disulfide and graphite are likely to be sedimented and may be sometimes coagulated with the lapse of time on the bottom of a treatment tank, thus making it difficult to disperse again. Therefore, it is difficult to perform a stable operation. Further, these two components may cause significant degradation of corrosion resistance, so that the resulting coating film is inferior in corrosion resistance as compared with the lubricating coating films of Patent Documents 1 to 3, to say nothing of the chemical conversion coating film.

In Patent Document 5, a coating film treatment agent containing a silicate (A) as a main component and containing excessively large amount of an anti-corrosive agent (D) is inferior in lubricity since seizure occurs under high extrusion load. Therefore, it becomes difficult to perform stable operation, thus failing to obtain sufficient long-term rust prevention property.

As mentioned above, the aqueous lubricating coating agent could not form a coating film having both of high corrosion resistance over a long term of about two or more months and workability during severe working, that are comparable to those of a chemical conversion coating film, even under service environment. If a silicate is included in the aqueous lubricating coating agent, there may arise a problem such as insufficient film removal.

Thus, it is an object of the present invention to provide a steel wire rod including a lubricating coating film, which can reconcile workabilities such as wire drawability, spike property, ball ironing property and film removability, and corrosion resistance such as long-term rust prevention property.

Means for Solving the Problems

The inventors of the present invention have intensively been studied so as to solve the above problems and found that it is possible to obtain high corrosion resistance and workability as well as sufficient adhesion and film removability that have never been achieved by each component alone, by adjustment of a ratio of a silicate to a tungstate are adjusted to a certain specific ratio, namely, adjustment of a mass ratio of water-soluble tungstate/water-soluble silicate to a predetermined ratio to form a composited lubricating coating film, and thus the present invention has been completed.

The present invention was structured in the following manner so as to solve the above problems.

The gist of the present invention lies in a steel wire rod including a lubricating coating film on a surface, wherein the lubricating coating film contains a water-soluble silicate and a water-soluble tungstate, a mass ratio of water-soluble tungstate/water-soluble silicate being in a range of 0.7 to 10, and contains no phosphorus.

The lubricating coating film is preferably formed using a composition prepared by mixing a water-soluble silicate and a water-soluble tungstate so as to adjust a mass ratio of water-soluble tungstate/water-soluble silicate in the lubricating coating film in a range of 0.7 to 10.

The lubricating coating film preferably contains a resin, and a mass ratio of resin/(water-soluble silicate+water-soluble tungstate) is preferably in a range of 0.01 to 1.5.

The resin is preferably at least one selected from a vinyl resin, an acrylic resin, an epoxy resin, a urethane resin, a phenol resin, a cellulose derivative, a polymaleic acid and a polyester resin.

The lubricating coating film preferably contains a lubricant, and a mass ratio of lubricant/(water-soluble silicate+water-soluble tungstate) is preferably in a range of 0.01 to 1.5.

The lubricant is preferably at least one selected from wax, polytetrafluoroethylene, fatty acid soap, fatty acid metal soap, fatty acid amide, molybdenum disulfide, tungsten disulfide, graphite and melamine cyanurate.

The mass of the coating film per unit area of the lubricating coating film is preferably in a range of 1.0 to 20 g/m².

Effects of the Invention

In the steel wire rod of the present invention, a lubricating coating film is structured in the manner mentioned above, thus obtaining a steel wire rod that has excellent workabilities such as wire drawability, spike property, ball ironing property and film removability, and corrosion resistance such as long-term rust prevention property. The lubricating coating film in the present invention is far better than a conventional aqueous lubricating coating film in that all of these performances are equal to or better than those of steel wire rods having a chemical conversion coating film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows evaluation criteria for seizure when ball ironing property is evaluated.

MODE FOR CARRYING OUT THE INVENTION

The present invention is directed to a steel wire rod including a lubricating coating film on a surface, wherein the lubricating coating film contains a water-soluble silicate and a water-soluble tungstate, a mass ratio of water-soluble tungstate/water-soluble silicate being in a range of 0.7 to 10, and contains no phosphorus.

In the present invention, a steel used in the steel wire rod also includes a carbon steel, an alloy steel, a special steel, and the like. Examples of such steel include a mild steel having a carbon content of 0.2% by mass or less (not including 0% by mass), a carbon steel having a carbon content of exceeding 0.2% by mass and 1.5% by mass or less, and an alloy or special steel containing at least one selected from silicon, manganese, phosphorus, sulfur, nickel, chromium, copper, aluminum, molybdenum, vanadium, cobalt, titanium, zircon, and the like according to the application of the mild steel or carbon steel. In the present invention, the steel wire rod generally refers to those obtained by forming a steel into a wire rod through hot working. The steel wire is included in the steel wire rod of the present invention. The steel wire refers to those obtained by further subjecting a steel wire rod to a working treatment, such as those obtained by drawing a steel wire rod into a wire having a specified size (wire diameter, circularity, etc.) and those obtained by subjecting a steel wire rod or a steel wire drawn into a wire to a plating treatment.

The steel wire rod of the present invention is not particularly limited as long as it is excellent in corrosion resistance and workability because of having the below-mentioned lubricating coating film, and a film, namely, an undercoating film may be further formed between a surface of the steel wire rod and the lubricating coating film. Both of these films may be a single layer, or a layer composed of two or more layers.

The lubricating coating film and the undercoating film contain no phosphorus, and a lubricating coating agent used for formation of the film does not contain a component containing phosphorus. However, in the present invention, it is not excluded that a component containing phosphorus is inevitably included in a coating film of a surface of the steel wire rod in the operation process. Namely, even if phosphorus as inevitable impurities may cause contamination in the actual operation, there is little possibility that phosphorus causes brittle fracture of a steel wire rod when the content of phosphorus is about 1% by mass or less, and thus it is possible to consider that phosphorizing does not occur.

A description will be made in order below from each component and composition of the lubricating coating film in the steel wire rod according to the present invention.

There is a need for the steel wire rod of the present invention to have a lubricating coating film on a surface, the lubricating coating film containing a water-soluble silicate and a water-soluble tungstate, and a mass ratio of water-soluble tungstate/water-soluble silicate being in a range of 0.7 to 10. When containing the water-soluble silicate and the water-soluble tungstate within the above range, it is possible to form a lubricating coating film having high corrosion resistance and workability as well as sufficient adhesion and film removability that have never been achieved by the water-soluble silicate or the water-soluble tungstate alone, or the other aqueous inorganic salt.

For example, the below-mentioned water-soluble silicate and water-soluble tungstate are composited to form a lubricating coating film, the water-soluble tungstate is incorporated into a network structure formed of the water-soluble silicate. As mentioned above, drawbacks of the water-soluble tungstate depend heavily on formation of a crystalline coating film and it becomes possible for the water-soluble tungstate to exist uniformly and finely by incorporating into the network structure of the water-soluble silicate. Whereby, it is possible to reconcile a property of being less likely to transmit moisture of the water-soluble silicate and a passive film having a self-repair function of the water-soluble tungstate, leading to a remarkable improvement in corrosion resistance.

Examples of the influence of the water-soluble tungstate on the water-soluble silicate include an improvement in workability and film removability. As mentioned above, the water-soluble silicate is inferior in workability and film removability since a firm continuous film is formed by polymerization of the water-soluble silicate. The composited water-soluble tungstate exists in the network structure of the water-soluble silicate, whereby, formation of a firm network structure is appropriately suppressed, thus enabling an improvement in workability and film removability.

To exhibit the performances mentioned above, a ratio of the amount of the water-soluble tungstate to that of the water-soluble silicate is important. A mass ratio of water-soluble tungstate/water-soluble silicate in the lubricating coating film is 0.7 or more, preferably 0.9 or more, and more preferably 1.1 or more. The mass ratio is 10 or less, preferably 6.0 or less, and more preferably 3.0 or less. If the mass ratio of water-soluble tungstate/water-soluble silicate is less than 0.7, the obtained film can achieve neither sufficient corrosion resistance nor workability, and is also inferior in film removability. This is because the amount of tungsten relatively decreases, thus failing to sufficiently form a passive film, while the amount of silicate relatively increases to form a firm network structure. If the mass ratio of water-soluble tungstate/water-soluble silicate is more than 10, the obtained film can achieve neither sufficient corrosion resistance nor workability. This is because the amount of the water-soluble silicate relatively decreases, thus making it easier to transmit moisture, while crystals of tungsten are precipitated, thus degrading adhesion and uniformity of the coating film.

As mentioned above, when a water-soluble silicate and a water-soluble tungstate are composited at an appropriate ratio, the synergy effect thereof enables realization of high workability and high corrosion resistance in the service environment, that has never been realized by the prior art, and formation of the lubricating coating film having sufficient film removability. When the lubricating coating film is formed, a lubricating coating agent containing a water-soluble silicate and a water-soluble tungstate may be prepared, followed by application to a surface of a steel wire rod. After application of the lubricating coating agent (namely, after a lubricating coating treatment), a mass ratio of water-soluble tungstate/water-soluble silicate in the lubricating coating film is the same as that of water-soluble tungstate/water-soluble silicate in the lubricating coating agent.

In the present invention, the lubricating coating film may be formed using a composition prepared by mixing a water-soluble silicate and a water-soluble tungstate so as to adjust a mass ratio of water-soluble tungstate/water-soluble silicate in the lubricating coating film in a range of 0.7 to 10.

In the lubricating coating film, a mass ratio tungsten/silicon is preferably 1.3 or more, more preferably 1.8 or more, and still more preferably 2.0 or more. The mass ratio is preferably 18 or less, more preferably 10 or less, and still more preferably 5.4 or less.

If the mass ratio of tungsten/silicon is less than 1.3, the obtained film can achieve neither sufficient corrosion resistance nor workability, and is also inferior in film removability. This is because the amount of the tungstate relatively decreases, thus failing to sufficiently form a passive film, while the amount of the silicate relatively increases to form a firm network structure. If the mass ratio of tungsten/silicon is more than 18, the obtained film can achieve neither sufficient corrosion resistance nor workability. This is because the amount of the silicate relatively decreases, thus making it easier to transmit moisture, while crystals of tungsten are precipitated, thus degrading adhesion and uniformity of the film. In the present invention, the mass ratio of tungsten/silicon is based on a ratio of tungsten element derived from the water-soluble tungstate to a silicon element derived from the water-soluble silicate in the film and can be calculated, for example, using inductively coupled plasma or fluorescent X-ray spectroscopy.

Examples of the water-soluble silicate used in the lubricating coating agent include lithium silicate, sodium silicate and potassium silicate. These water-soluble silicates may be used alone, or two or more water-soluble silicates may be used.

Examples of the water-soluble tungstate used in the lubricating coating agent include lithium tungstate, sodium tungstate, potassium tungstate, and ammonium tungstate. These water-soluble tungstates may be used alone, or two or more water-soluble tungstates may be used.

A resin will be described below. The resin is mixed in the coating film for the purpose of the binder effect, an improvement in adhesion between a base material and a film, imparting of leveling property by the thickening effect, and stabilization of a dispersion component. Examples of the resin having such function and property include a vinyl resin, an acrylic resin, an epoxy resin, a urethane resin, a phenol resin, a cellulose derivative, a polymaleic acid and a polyester resin. These resins may be used alone, or two or more resins may be used in combination.

In the present invention, the lubricating coating film contains a resin and a mass ratio of resin/(water-soluble silicate and water-soluble tungstate) is preferably 0.01 or more, and more preferably 0.05 or more. The mass ratio is preferably 1.5 or less, and more preferably 1.0 or less. If the mass ratio is less than 0.01, the above effects are not sufficiently exerted. Meanwhile, if the mass ratio exceeds 1.5, the amounts of the water-soluble silicate and the water-soluble tungstate relatively decrease, thus failing to realize sufficient workability and corrosion resistance.

A lubricant will be described below. The lubricant itself has slipperiness, and has a function of reducing a friction force. In general, if the friction force increases during plastic working, an increase in working energy, heat generation, seizure, and the like occur. It the lubricant is included in a lubricating coating agent used in the present invention, the lubricant exists in a lubricating coating film in the form of a solid, thus suppressing an increase in friction force. Examples of the lubricant having such function and property include wax, polytetrafluoroethylene, fatty acid soap, fatty acid metal soap, fatty acid amide, molybdenum disulfide, tungsten disulfide, graphite and melamine cyanurate. These lubricants may be used alone, or two or more lubricants may be used in combination.

Specific examples of the wax include polyethylene wax, paraffin wax, microcrystalline wax, polypropylene wax, and carnauba wax. Specific examples of the fatty acid soap include sodium myristate, potassium myristate, sodium palmitate, potassium palmitate, sodium stearate and potassium stearate. Specific examples of the fatty acid metal soap include calcium stearate, zinc stearate, barium stearate, magnesium stearate, and lithium stearate. The fatty acid amide is, for example, an amide compound having two fatty acids, and specific examples thereof include ethylenebislauric acid amide, ethylenebisstearic acid amide, ethylenebisbehenic acid amide, N,N′-distearyladipic acid amide, ethylenebisoleic acid amide, ethylenebiserucic acid amide, hexamethylenebisoleic acid amide, and N,N′-dioleyladipic acid amide.

When the lubricating coating film is mixed with the lubricant, the mass ratio of lubricant/(water-soluble silicate and water-soluble tungstate) is preferably 0.01 or more, and more preferably 0.05 or more, and the mass ratio is preferably 1.5 or less, and more preferably 1.0 or less. Here, if the mass ratio of lubricant/(water-soluble silicate+water-soluble tungstate) is less than 0.01, it is impossible to perform performances because of too small amount of the lubricant. If the mass ratio exceeds 1.5, the amounts of the water-soluble silicate and the water-soluble tungstate relatively decrease, thus failing to exhibit high corrosion resistance and workability which are features of the present invention.

The lubricating coating film of the steel wire rod of the present invention can be mixed with a viscosity modifier, in addition to the water-soluble silicate, the water-soluble tungstate, the resin, and the lubricant, for the purpose of imparting leveling property and thixotrophy so as to ensure a uniform coating state when a lubricating treatment solution is applied to a base material. The amount of the viscosity modifier is preferably in a range of 0.1 to 30% by mass based on the mass of total solid component. Specific examples of the viscosity modifier include smectite-based clay minerals such as montmorillonite, sauconite, beidellite, hectorite, nontronite, saponite, iron-rich saponite, and stevensite; and inorganic thickeners such as pulverized silica, bentonite, and kaolin.

The lubricating coating film may contain water-soluble salts, for example, inorganic salts, such as sulfates and borates, and organic salts so as to improve adhesion and workability. Examples of the sulfate include sodium sulfate, potassium sulfate, and the like. Examples of the borate include sodium metaborate, potassium metaborate, ammonium metaborate, and the like.

Examples of the organic salt include salts of formic acid, acetic acid, butyric acid, oxalic acid, succinic acid, lactic acid, ascorbic acid, tartaric acid, citric acid, malic acid, malonic acid, maleic acid, phthalic acid, and the like, with alkali metals, alkali earth metals, and the like.

The lubricating coating film of the steel wire rod of the present invention can be imparted with high corrosion resistance before and after working, and may be mixed with other water-soluble rust preventives and inhibitors for the purpose of further improving corrosion resistance. Specifically, it is possible to use known rust preventives and inhibitors, for example, various organic acids such as oleic acid, dimer acid, tartaric acid, and citric acid; various chelating agents such as EDTA, NTA, HEDTA, and DTPA; mixed components of alkanolamine such as triethanolamine, and amine salts of p-t-butylbenzoic acid; and combinations of a carboxylic acid amine salt, a dibasic acid amine salt, an alkenylsuccinic acid, and a water-soluble salt thereof with aminotetrazole and a water-soluble salt thereof. These rust preventives and inhibitors may be used alone, or two or more rust preventives and inhibitors may be used in combination. The amount is preferably in a range of 0.1 to 30% by mass based on the mass of total solid component.

In the present invention, the lubricating coating agent contains the water-soluble silicate and the water-soluble tungstate as essential components, and optionally contains the above-mentioned resin, lubricant, and water-soluble salts.

The amount of the water-soluble silicate preferably exceeds 5% by mass, more preferably 10% by mass or more, and still more preferably 15% by mass or more, and is also preferably 58% by mass or less, more preferably 52% by mass or less, and still more preferably 45% by mass or less, in 100% by mass of the lubricating coating agent.

The amount of the water-soluble tungstate is preferably 10% by mass or more, more preferably 15% by mass or more, and still more preferably 20% by mass or more, and is also preferably 91% by mass or less, more preferably 85% by mass or less, and still more preferably 80% by mass or less, in 100% by mass of the lubricating coating agent.

If the amount of the water-soluble silicate is 5% by mass or less and the amount of the water-soluble tungstate exceeds 91% by mass, the obtained film cannot achieve sufficient long-term rust prevention property, and is inferior in wire drawability and ball ironing property. This is because the amount of the water-soluble silicate relatively decreases, thus making it easier to transmit moisture, while crystals of tungsten are precipitated, thus degrading adhesion and uniformity of the coating film. If the amount of the water-soluble silicate exceeds 58% by mass and the amount of the water-soluble tungstate is less than 10% by mass, the obtained film can achieve neither sufficient corrosion resistance nor workability. This is because the amount of tungsten relatively decreases, thus failing to sufficiently form a passive film, while the amount of silicate relatively increases to form a firm network structure.

In the present invention, the lubricating coating film may also be formed as a lubricating undercoating film for dry lubricant. Use as an undercoating film of a dry lubricant enables leveling up of lubricity, seize resistance, and corrosion resistance. There is no limitation on the dry lubricant and it is possible to use, for example, a general lubricating powder or wire drawing powder which contains, as main components, higher fatty acid soap, borax, lime, molybdenum disulfide, and the like.

In the present invention, a liquid medium (solvent, dispersion medium) for formation of a lubricating coating film in a film treatment agent is water. To shorten the drying time of the lubricant in the drying step, it is possible to mix with an alcohol having a boiling point lower than that of water.

To enhance stability of the solution, the lubricating coating agent may contain a water-soluble strong alkali component. Specific examples thereof include lithium hydroxide, sodium hydroxide and potassium hydroxide. These water-soluble strong alkali components may be used alone, or two or more water-soluble strong alkali components may be used in combination. The amount of these water-soluble strong alkali components is preferably in a range of 0.01 to 10% by mass based on the mass of total solid component.

The lubricating coating agent used in the present invention is produced by adding a water-soluble silicate and a water-soluble tungstate, and a resin and a lubricant, and if necessary a viscosity modifier to water as a liquid medium, followed by mixing. The water-soluble silicate and the water-soluble tungstate used herein are soluble in water, but some of the resin, the lubricant, the viscosity modifier, and the like are insoluble or slightly soluble in water, so that there is a need to disperse them in the lubricating coating agent. They are dispersed by a method in which a surfactant capable of serving as a dispersant is optionally added to water and, after sufficiently maintaining the surfactant in close association with water, stirring is continued until a dispersed state becomes uniform. Stirring is performed by a general method such as propeller stirring or stirring with a homogenizer. To obtain a stable dispersed state, known surfactants can be used.

A method for producing a steel wire rod according to the present invention will be described below. The method according to the present invention includes a cleaning step of a steel wire rod, a production step of a film treatment agent, and a drying step. Each step will be described below.

Cleaning Step (Pretreatment Step)

Before formation of a lubricating coating film on a steel wire rod, at least one cleaning treatment selected from shot blasting, sand blasting, wet blasting, peeling, alkali degreasing, and pickling is preferably performed. Cleaning as used herein is performed for the purpose of removing oxide scales grown by annealing, and various contaminations (oils, etc.).

Production Step of Lubricating Coating Film

In the present invention, there is no particular limitation on a production step of a lubricating coating film on a steel wire rod, and it is possible to use coating methods such as an immersion method, a flow coating method, and a spraying method. Coating is not particularly limited as long as a surface of the steel wire rod is sufficiently coated with a lubricating coating agent of the present invention, and also the coating time is not particularly limited. To enhance drying property in this case, the steel wire rod may be brought into contact with the lubricating coating agent after heating to a temperature in a range of 60 to 80° C. The steel wire rod may also be brought into contact with the lubricating coating agent heated to a temperature in a range of 40 to 70° C. Whereby, the drying property may be sometimes improved significantly, thus enabling drying at a normal temperature and reduction in thermal energy loss.

Drying Step

There is a need to dry the lubricating coating agent. Drying may be performed by being left to stand at a normal temperature, or may performed at 60 to 150° C. for 1 to 30 minutes.

The mass of a lubricating coating film formed on a steel wire rod is appropriately controlled by the degree of subsequent working, and the mass of the coating film is preferably 1.0 g/m² or more, more preferably 2.0 g/m² or more, and is also preferably 20 g/m² or less, and more preferably 15 g/m² or less. Low mass of the coating film leads to insufficient workability. It is not preferred that the mass of the coating film exceeds 20 g/m² since clogging occurs in a die, although there is no problem in workability. The mass of the coating film can be calculated from a difference in mass between steel wire rods before and after a treatment, and a surface area. To control so as to adjust in a range of the above-mentioned mass of the coating film, the solid component mass (concentration) of the lubricating coating agent is appropriately adjusted. In practice, after diluting a high concentration lubricant with water, the thus obtained treatment solution is often used. There is no particular limitation on water used for dilution and adjustment, and, for example, pure water, deionized water, tap water, ground water, industrial water, and the like can be used.

Film Removal Method

In the present invention, film removal can be performed by immersing the lubricating coating film formed of the lubricating coating agent in an aqueous alkali cleaner, or spraying the aqueous alkali cleaner. The alkali cleaner is a solution prepared by dissolving a common alkali component such as sodium hydroxide or potassium hydroxide in water and, when the alkali cleaner is brought into contact with the lubricating coating film, the lubricating coating film dissolves in the cleaning solution, thus making it possible to easily perform film removal. It is also possible to obtain a film capable of easily falling off by a heat treatment after working. Therefore, alkali cleaning and heat treatment enable prevention of contamination and poor plating in the subsequent step caused by insufficient film removal.

EXAMPLES

The present invention will be described below in a more specific manner by way of Examples and Comparative

Examples, together with effects thereof, with respect to a steel wire rod. The present invention is not limited to these Examples. In the following description, parts are by mass and percentages are by mass, unless otherwise specified.

(1-1) Preparation of Lubricating Coating Agent

In accordance with the combination and proportion shown in Table 1, lubricating coating agents of Examples 1 to 18 and Comparative Examples 1 to 12 were prepared using the respective components shown in Table 1. Comparative Example 13 means the case subjected to a phosphate/soap treatment.

<Water-Soluble Silicate>

(A-1) Sodium metasilicate (A-2) JIS No. 3 sodium silicate (Na₂O.nSiO₂, n=3) (A-3) Lithium silicate (Li₂O.nSiO₂, n=3.5)

<Water-Soluble Tungstate>

(B-1) Ammonium tungstate (B-2) Sodium tungstate (B-3) Lithium tungstate

<Resin>

(C-1) Polyvinyl alcohol (average molecular weight of about 50,000) (C-2) Sodium neutralizing salt of isobutylene-maleic anhydride copolymer (average molecular weight of about 165,000)

<Lubricant>

(D-1) Anionic polyethylene wax (average particle size of 5 μm) (D-2) Ethylenebis-stearic acid amide

<Water-Soluble Salt>

(E-1) Sodium metaborate (E-2) Sodium tartrate (E-3) Sodium sulfate (E-4) Sodium pyrophosphate

<Undercoating Film>

(F-1) Zirconium chemical conversion treatment agent (PALLUCID (registered trademark) 1500, manufactured by Nihon Parkerizing Co., Ltd.)

TABLE 1 Water-soluble silicate Water-soluble tungstate Resin Lubricant Undercoating Component (A) Component (B) Component (C) Component (D) film (A-1) (A-2) (A-3) (B-1) (B-2) (B-3) (C-1) (C-2) (D-1) (D-2) (F-1) Example 1 40 15 0 45 0 0 0 0 0 0 None Example 2 0 25 0 0 75 0 0 0 0 0 None Example 3 30 20 5 0 0 45 0 0 0 0 None Example 4 9 0 0 25 30 30 6 0 0 0 None Example 5 10 0 30 38 0 0 2 0 20 0 None Example 6 0 0 20 0 30 20 0 10 10 10 None Example 7 40 0 0 0 50 0 7 0 0 3 None Example 8 0 45 0 0 20 30 0 0 5 0 None Example 9 10 0 5 17 0 10 18 0 20 20 None Example 10 15 15 0 0 23 0 0 0 24 23 None Example 11 0 10 10 10 10 0 15 25 0 20 None Example 12 5 0 0 0 35 0 5 40 15 0 None Example 13 10 30 0 40 0 20 0 0 0 0 None Example 14 0 0 15 0 0 65 20 0 0 0 None Example 15 30 10 0 0 40 0 0 0 5 15 None Example 16 10 30 0 20 40 0 0 0 0 0 Exist Example 17 30 10 10 0 0 50 0 0 0 0 Exist Example 18 15 0 0 60 25 0 0 0 0 0 Exist Comparative Example 1 No coating film (only dry lubricant) Comparative Example 2 65 0 0 35 0 0 0 0 0 0 None Comparative Example 3 0 7 0 93 0 0 0 0 0 0 None Comparative Example 4 0 100 0 0 0 0 0 0 0 0 None Comparative Example 5 0 0 0 0 0 90 10 0 0 0 None Comparative Example 6 0 0 0 60 0 0 0 15 0 0 None Comparative Example 7 0 0 0 0 35 30 10 0 0 0 None Comparative Examole 8 50 15 0 0 0 0 0 0 0 0 None Comparative Example 9 0 55 15 0 0 0 0 0 0 0 None Comparative Example 10 0 0 0 0 0 0 0 20 0 0 None Comparative Example 11 0 0 0 0 0 0 5 0 0 0 None Comparative Example 12 0 0 0 0 0 0 0 10 0 0 None Comparative Example 13 Phosphate/soap treatment Mass of Mass ratio of film per unit resin/(water- Mass ratio of area of Mass ratio of soluble lubricant/(water- Water-soluble salt lubricating water-soluble tungstate + soluble tungstate + Component (E) coating film tungstate/water- water-soluble water-soluble (E-1) (E-2) (E-3) (E-4) (g/m²) soluble silicate) silicate) silicate) Example 1 0 0 0 0 15.0 0.82 — — Example 2 0 0 0 0 3.0 3.00 — — Example 3 0 0 0 0 1.2 0.82 — — Example 4 0 0 0 0 7.7 9.44 0.06 — Example 5 0 0 0 0 6.6 0.95 0.03 0.26 Example 6 0 0 0 0 7.0 2.50 0.14 0.29 Example 7 0 0 0 0 20.0 1.25 0.08 0.03 Example 8 0 0 0 0 5.5 1.11 — 0.05 Example 9 0 0 0 0 4.2 1.80 0.43 0.95 Example 10 0 0 0 0 3.8 0.77 — 0.89 Example 11 0 0 0 0 3.9 1.00 1.00 0.50 Example 12 0 0 0 0 2.2 7.00 1.13 0.38 Example 13 0 0 0 0 7.1 1.50 — — Example 14 0 0 0 0 7.8 4.33 0.25 — Example 15 0 0 0 0 5.9 1.00 — 0.25 Example 16 0 0 0 0 6.5 1.50 — — Example 17 0 0 0 0 7.5 1.00 — — Example 18 0 0 0 0 8.5 5.67 — — Comparative Example 1 No coating film (only dry lubricant) Comparative Example 2 0 0 0 0 3.0 0.54 — — Comparative Example 3 0 0 0 0 1.8 13.29 — — Comparative Example 4 0 0 0 0 3.0 — — — Comparative Example 5 0 0 0 0 5.1 — 0.11 — Comparative Example 6 25 0 0 0 7.7 — 0.25 — Comparative Example 7 0 25 0 0 6.3 — 0.15 — Comparative Examole 8 0 10 25 0 5.5 — — — Comparative Example 9 0 0 0 30 5.6 — — — Comparative Example 10 40 0 0 40 — — — — Comparative Example 11 95 0 0 0 — — — — Comparative Example 12 0 90 0 0 — — — — Comparative Example 13 Phosphate/soap treatment *Numerical in each of components (A) to (E) means an addition amount in a lubricating coating agent (% by mass).

(1-2) Lubricating Coating Treatment

Each lubricating coating treatment was carried out by the following steps, with respect to a surface of a φ3.2 mm sample steel wire rod (steel type: S45C). After subjecting to the lubricating coating treatment, a mass ratio of water-soluble tungstate/water-soluble silicate in a lubricating coating film of a sample steel wire rod is the same as a mass ratio of water-soluble tungstate/water-soluble silicate in a lubricating coating agent mentioned in Table 1.

Pretreatment and Lubricating Coating Treatment of Examples 1 to 15 and Comparative Examples 2 to 12

(a) Degreasing: commercially available degreasing agent (FINECLEANER (registered trademark) E6400, manufactured by Nihon Parkerizing Co., Ltd.), concentration: 20 g/L, temperature: 60° C., immersion: 10 minutes (b) Water rinsing: tap water, normal temperature, immersion: 20 seconds (c) Pickling: 17.5% hydrochloric acid, normal temperature, immersion: 20 minutes (d) Water rinsing: tap water, normal temperature, immersion: 20 seconds (e) Neutralization: commercially available neutralizer (PREPALENE (registered trademark) 27, manufactured by Nihon Parkerizing Co., Ltd.) (f) Lubricating coating treatment: lubricating coating agent prepared in (1-1), temperature: 60° C., immersion: 1 minute (g) Drying: at 100° C. for 10 minutes (h) The amount of a lubricating coating film was appropriately adjusted by the concentration of a treatment agent.

Pretreatment and Lubricating Coating Treatment of Examples 16 to 18

(a) Degreasing: commercially available degreasing agent (FINECLEANER (registered trademark) 6400, manufactured by Nihon Parkerizing Co., Ltd.), concentration: 20 g/L, temperature: 60° C., immersion: 10 minutes (b) Water rinsing: tap water, normal temperature, immersion: 30 seconds (c) Pickling: hydrochloric acid, concentration: 17.5%, normal temperature, immersion: 10 minutes (d) Water rinsing: tap water, normal temperature, immersion: 30 seconds (e) Zirconium treatment: commercially available zirconium chemical conversion treatment agent (PALLUCID (registered trademark) 1500, manufactured by Nihon Parkerizing Co., Ltd.), concentration: 50 g/L, temperature: 45° C., immersion: 2 minutes (f) Water rinsing: tap water, normal temperature, immersion: 30 seconds (g) Lubricating coating treatment: lubricating coating agent prepared in (1-1), temperature 60° C., immersion: 1 minute (h) Drying: 100° C., 10 minutes (i) Amount of undercoating film: zirconium undercoat: 50 mg/m²

The amount of a lubricating coating film was appropriately adjusted by the concentration of a treatment agent.

Treatment of Comparative Example 1

(a) Degreasing: commercially available degreasing agent (FINECLEANER (registered trademark) 6400, manufactured by Nihon Parkerizing Co., Ltd.), concentration: 20 g/L, temperature: 60° C., immersion: 10 minutes (b) Water rinsing: tap water, normal temperature, immersion: 30 seconds (c) Pickling: hydrochloric acid, concentration: 17.5%, normal temperature, immersion: 10 minutes (d) Water rinsing: tap water, normal temperature, immersion: 30 seconds (e) Pure water rinsing: deionized water, normal temperature, immersion: 30° C. (f) Drying: at 100° C. for 10 minutes

Pretreatment and Film Treatment of Comparative Example 13 (Phosphate/Soap Treatment)

(a) Degreasing: commercially available degreasing agent (FINECLEANER (registered trademark) 6400, manufactured by Nihon Parkerizing Co., Ltd.), concentration: 20 g/L, temperature: 60° C., immersion: 10 minutes (b) Water rinsing: tap water, normal temperature, immersion: 30 seconds (c) Pickling: hydrochloric acid, concentration 17.5%, normal temperature, immersion: 10 minutes (d) Water rinsing: tap water, normal temperature, immersion: 30 seconds (e) Chemical conversion treatment: commercially available zinc phosphate chemical conversion treatment agent (PALBOND (registered trademark) 3696X, manufactured by Nihon Parkerizing Co., Ltd.) concentration 75 g/L, temperature 80° C., immersion: 10 minutes (f) Water rinsing: tap water, normal temperature, immersion: 30 seconds (g) Soap treatment: commercially available reactive soap lubricant (PALUBE (registered trademark) 235, manufactured by Nihon Parkerizing Co., Ltd.), concentration: 70 g/L, temperature 85° C., immersion: 3 minutes (h) Drying: at 100° C. for 10 minutes (i) Amount of film: 10 g/m²

(1-3) Evaluation Test

(1-3-1) Workability (Wire Drawability) Test

Wire drawing was performed by drawing a sample wire rod in size of φ3.2 mm×20 m through a φ2.76 die. Missile C40 available from Matsuura Kougyo K.K. was used as a dry lubricant. Immediately before drawing a material, a die box was charged with the dry lubricant so that the dry lubricant naturally adheres to the material. Evaluation was made from seizure of the test material and the remaining amount of the lubricating coating film after wire drawing. In wire drawing of the phosphate/soap coating film of Comparative Example 13, the dry lubricant is not used in accordance with a normal usage manner.

Evaluation Criteria

A: No seizure occurs and no metal gloss is recognized and, on the whole, a film remains in a large amount. B: No seizure occurs and no metal gloss is recognized, and a film remains in an amount which slightly smaller than that in A. C: No seizure occurs and a film retention amount is slightly small, and metal gloss is partially recognized. D: No seizure occurs and metal gloss is recognized at numerous sites. E: Seizure occurred.

(1-3-2) Corrosion Resistance (Long-Term Rust Prevention Property) Test

In summer season, a wire rod subjected to the above-mentioned wire drawing test was exposed to an open air atmosphere indoors for two weeks or two months, and then the degree of rusting was observed. It was judged that the more the rust area increases, the more corrosion resistance becomes inferior.

Evaluation Criteria

A: Extremely excellent as compared with a phosphate/soap coating film (rust area of 3% or less) B: Excellent as compared with a phosphate/soap coating film (rust area of exceeding 3% to 10% or less) C: Equivalent to a phosphate/soap coating film (rust area of exceeding 10% to 20% or less) D: Inferior as compared with a phosphate/soap coating film (rust area of exceeding 20% to 30% or less) E: Drastically inferior as compared with a phosphate/soap coating film (rust area of exceeding 30%)

The test results are shown in Table 2. In all Examples, rusting is less likely to occur over a long term and satisfactory corrosion resistance is exhibited, and also a lubricating coating film remains in a large amount, resulting in satisfactory workability. As a result of subjecting to a zirconium chemical conversion treatment as a surface treatment, higher corrosion resistance was exhibited. In Comparative Example 1 which is an example in which a lubricating coating film used in Examples is not formed, seizure occurred during wire drawing and rusting frequently occurred in both cases where the wire rod was exposed to an open air atmosphere for two weeks and two months, thus failing to reach a practical level. In Comparative Examples 2 to 9 in which a ratio of a water-soluble silicate to a water-soluble tungstate deviates from the scope of the present invention, workability was inferior and also corrosion resistance was inferior because of small film retention amount after wire drawing. In Comparative Examples 10 to 12 in which components other than the silicate and tungstate were included as aqueous inorganic salts, workability was inferior and also corrosion resistance was inferior because of small film retention amount after wire drawing. In Comparative Example 13 in which the phosphate coating film was subjected to a reactive soap treatment, comparatively excellent performances were exhibited. However, because of containing phosphorus, when subjecting to a heat treatment such as quenching and tempering while having the lubricating coating film on a surface, there is a fear that the steel wire rod becomes fragile as a result of the occurrence of phosphorizing. Therefore, Comparative Example 13 deviates from the object of the present invention. Similarly, Comparative Examples 9 and 10 deviate from the scope of the present invention because of containing phosphorus.

TABLE 2 Corrosion resistance Workability (Rust prevention property) (Wire Two Two Phosphatizing drawability) weeks months property*1 Example 1 B A B B Example 2 A A A B Example 3 B A B B Example 4 B A B B Example 5 B A A B Example 6 A A A B Example 7 A A A B Example 8 B A A B Example 9 A A A B Example 10 B A B B Example 11 B A A B Example 12 B A B B Example 13 A A A B Example 14 A A B B Example 15 A A B B Example 16 A A A B Example 17 B A A B Example 18 B A A B Comparative E E E B Example 1 Comparative C B D B Example 2 Comparative D B C B Example 3 Comparative D C C B Example 4 Comparative D D D B Example 5 Comparative D D D B Example 6 Comparative D D D B Example 7 Comparative C E E B Example 8 Comparative C E E E Example 9 Comparative D E E E Example 10 Comparative D E E B Example 11 Comparative E E E B Example 12 Comparative B B B E Example 13 *1B: There is no possibility of brittle fracture of a steel wire rod due to phosphorus because of containing no phosphorus. E: There is possibility of brittle fracture of a steel wire rod due to phosphorus because of containing phosphorus.

The present invention will be described below in a more specific manner by way of Examples and Comparative Examples, together with effects thereof, with respect to a steel wire. The present invention is not limited to these Examples. In the following description, parts are by mass and percentages are by mass, unless otherwise specified.

(2-1) Preparation of Lubricating Coating Agent

In accordance with the combination and proportion shown in Table 3, lubricating coating agents of Examples 19 to 38 and Comparative Examples 14 to 25 were prepared using the respective components shown below. Comparative Example 26 means the case subjected to a phosphate/soap treatment.

<Water-Soluble Silicate>

(A-1) Sodium metasilicate (A-2) JIS No. 3 sodium silicate (Na₂O.nSiO₂, n=3) (A-3) Lithium silicate (LiO.nSiO₂, n=3.5)

<Water-Soluble Tungstate>

(B-1) Ammonium tungstate (B-2) Sodium tungstate (B-3) Lithium tungstate

<Resin>

(C-1) Polyvinyl alcohol (average molecular weight of about 50,000) (C-2) Sodium neutralizing salt of isobutylene-maleic anhydride copolymer (average molecular weight of about 165,000) (C-3) Carboxymethylcellullose sodium (average molecular weight of about 30,000) (C-4) Aqueous nonionic urethane resin emulsion

<Lubricant>

(D-1) Anionic polyethylene wax (average particle size of 5 μm) (D-2) Ethylenebis-stearic acid amide (D-3) Calcium stearate (D-4) Polytetrafluoroethylene dispersion (average particle size of 0.2 μm)

<Water-Soluble Salt>

(E-1) Sodium metaborate (E-2) Sodium tartrate (E-3) Sodium sulfate (E-4) Sodium pyrophosphate

<Undercoating Film>

(F-1) Zirconium chemical conversion treatment agent (PALLUCID (registered trademark) 1500, manufactured by Nihon Parkerizing Co., Ltd.)

TABLE 3 Water-soluble silicate Water-soluble tungstate Resin Lubricant Undercoating Component (A) Component (B) Component (C) Component (D) film (A-1) (A-2) (A-3) (B-1) (B-2) (B-3) (C-1) (C-2) (C-3) (C-4) (D-1) (D-2) (D-3) (D-4) (F-1) Example 19 0 20 0 40 0 0 0 25 0 0 15 0 0 0 None Example 20 25 0 0 20 0 0 0 40 0 5 10 0 0 0 None Example 21 5 20 0 0 0 35 20 0 0 0 0 0 20 0 None Example 22 21 10 5 18 21 0 0 0 0 5 10 10 0 0 None Example 23 0 15 0 0 0 45 0 0 10 0 0 10 0 20 None Example 24 20 0 10 0 50 0 10 0 0 0 10 0 0 0 None Example 25 0 25 0 0 0 21 0 25 12 0 0 0 7 10 None Example 26 0 0 15 65 0 0 0 0 0 0 0 0 0 20 None Example 27 0 40 0 0 40 0 15 0 0 0 5 0 0 0 None Example 28 9 18 25 37 0 0 0 0 0 2 0 0 9 0 None Example 29 0 10 5 0 15 10 0 30 0 10 10 10 0 0 None Example 30 5 0 0 0 50 0 0 15 10 0 10 0 0 10 None Example 31 0 25 0 10 8 0 5 0 0 0 20 10 0 20 None Example 32 10 32 0 15 27 0 10 0 0 0 8 0 0 0 None Example 33 0 10 0 0 40 20 0 20 0 0 10 0 0 0 None Example 34 0 24 0 0 23 0 0 11 0 0 5 20 0 17 None Example 35 0 15 15 30 0 0 10 0 0 10 0 0 10 10 None Example 36 20 0 0 10 30 0 0 0 15 0 10 5 0 10 Exist Example 37 0 20 10 0 25 0 0 30 0 5 10 0 0 0 Exist Example 38 0 10 0 0 30 25 20 0 0 0 0 0 15 0 Exist Comparative Example 14 50 0 0 0 0 0 0 10 20 0 0 0 20 0 None Comparative Example 15 0 0 0 60 0 0 20 0 0 0 0 20 0 0 None Comparative Example 16 0 0 37 0 0 15 0 0 0 13 35 0 0 0 None Comparative Example 17 0 2 0 0 50 0 0 20 0 15 0 0 0 13 None Comparative Example 18 45 0 0 0 0 0 0 0 15 0 0 0 15 0 None Comparative Example 19 0 20 20 0 0 0 10 0 0 20 0 0 10 10 None Comparative Example 20 0 0 0 40 0 0 0 15 0 0 20 0 0 0 None Comparative Example 21 0 0 0 0 50 0 10 0 5 0 5 0 10 0 None Comparative Example 22 0 0 0 0 0 0 0 5 0 0 0 10 0 25 None Comparative Example 23 0 0 0 0 0 0 10 0 0 10 0 20 0 0 None Comparative Example 24 0 0 0 0 0 0 0 0 25 0 0 25 0 0 None Comparative Example 25 0 0 0 0 0 0 0 25 0 0 15 0 20 0 None Comparative Example 26 Phosphate/soap treatment Mass of film Mass ratio of Mass ratio of per unit area Mass ratio of resin/(water- lubricant/(water- Water-soluble salt of lubricating water-soluble soluble tungstate + soluble tungstate + Component (E) coating film tungstate/water- water-soluble water-soluble (E-1) (E-2) (E-3) (E-4) (g/m²) soluble silicate) silicate) silicate) Example 19 0 0 0 0 11.1 2.00 0.42 0.25 Example 20 0 0 0 0 12.5 0.80 1.00 0.22 Example 21 0 0 0 0 10.5 1.40 0.33 0.33 Example 22 0 0 0 0 1.0 1.08 0.07 0.27 Example 23 0 0 0 0 10.0 3.00 0.17 0.50 Example 24 0 0 0 0 2.2 1.67 0.13 0.13 Example 25 0 0 0 0 3.5 0.84 0.80 0.37 Example 26 0 0 0 0 7.7 4.33 — 0.25 Example 27 0 0 0 0 9.7 1.00 0.19 0.06 Example 28 0 0 0 0 9.2 0.71 0.02 0.10 Example 29 0 0 0 0 8.9 1.67 1.00 0.50 Example 30 0 0 0 0 10.2 10.00  0.45 0.36 Example 31 2 0 0 0 5.5 0.72 0.12 1.16 Example 32 0 3 0 0 8.9 1.00 0.12 0.10 Example 33 0 0 0 0 19.5 6.00 0.29 0.14 Example 34 0 0 0 0 16.9 0.96 0.23 0.89 Example 35 0 0 0 0 19.9 1.00 0.33 0.33 Example 36 0 0 0 0 10.1 2.00 0.25 0.42 Example 37 0 0 0 0 6.6 0.83 0.64 0.18 Example 38 0 0 0 0 5.5 5.50 0.31 0.23 Comparative Example 14 0 0 0 0 12.8 — 0.60 0.40 Comparative Example 15 0 0 0 0 13.3 — 0.33 0.33 Comparative Example 16 0 0 0 0 3.9 0.41 0.25 0.67 Comparative Example 17 0 0 0 0 3.9 25.00  0.67 0.25 Comparative Example 18 0 0 25 0 11.1 — 0.33 0.33 Comparative Example 19 0 0 0 10 10.8 — 0.75 0.50 Comparative Example 20 25 0 0 0 9.2 — 0.38 0.50 Comparative Example 21 10 10 0 0 6.2 — 0.30 0.30 Comparative Example 22 30 0 0 30 — — — — Comparative Example 23 0 40 20 0 — — — — Comparative Example 24 50 0 0 0 — — — — Comparative Example 25 0 40 0 0 — — — — Comparative Example 26 Phosphate/soap treatment *Numerical in each of components (A) to (E) means an addition amount in a lubricating coating agent (% by mass). For a phosphate/soap treatment, a film removal method is different from that for an aqueous lubricant, film removability was not evaluated.

(2-2) Lubricating Coating Treatment

For evaluation on the hypothesis of a bolt production step to be the object of working of a steel wire, various test pieces were subjected to the following lubricating coating treatment. After subjecting to the lubricating coating treatment, a mass ratio of water-soluble tungstate/water-soluble silicate in a lubricating coating film of a sample steel wire rod is the same as a mass ratio of water-soluble tungstate/water-soluble silicate in a lubricating coating agent mentioned in Table 3.

Pretreatment and Lubricating Coating Treatment of Examples 19 to 35 and Comparative Examples 14 to 25

(a) Degreasing: commercially available degreasing agent (FINECLEANER (registered trademark) E6400, manufactured by Nihon Parkerizing Co., Ltd.), concentration: 20 g/L, temperature: 60° C., immersion: 10 minutes (b) Water rinsing: tap water, normal temperature, immersion: 20 seconds (c) Pickling: 17.5% hydrochloric acid, normal temperature, immersion: 20 minutes (d) Water rinsing: tap water, normal temperature, immersion: 20 seconds (e) Neutralization: commercially available neutralizer (PREPALENE (registered trademark) 27, manufactured by Nihon Parkerizing Co., Ltd.) (f) Lubricating coating treatment: lubricating coating agent prepared in (2-1), temperature: 60° C., immersion: 1 minute (g) Drying: at 100° C. for 10 minutes (h) The amount of a lubricating coating film was appropriately adjusted by the concentration of a treatment agent.

Pretreatment and Lubricating Coating Treatment of Examples 36 to 38

(a) Degreasing: commercially available degreasing agent (FINECLEANER (registered trademark) 6400, manufactured by Nihon Parkerizing Co., Ltd.), concentration: 20 g/L, temperature: 60° C., immersion: 10 minutes (b) Water rinsing: tap water, normal temperature, immersion: 30 seconds (c) Pickling: hydrochloric acid, concentration: 17.5%, normal temperature, immersion: 10 minutes (d) Water rinsing: tap water, normal temperature, immersion: 30 seconds (e) Zirconium treatment: commercially available zirconium chemical conversion treatment agent (PALLUCID (registered trademark) 1500, manufactured by Nihon Parkerizing Co., Ltd.), concentration: 50 g/L, temperature: 45° C., immersion: 2 minutes (f) Water rinsing: tap water, normal temperature, immersion: 30 seconds (g) Lubricating coating treatment: lubricating coating agent prepared in (2-1), temperature: 60° C., immersion: 1 minute (h) Drying: at 100° C. for 10 minutes (i) Amount of undercoating film: zirconium undercoat: 50 mg/m²

The amount of a lubricating coating film was appropriately adjusted by the concentration of a treatment agent.

Pretreatment and Film Treatment of Comparative Example 26 (Phosphate/Soap Treatment)

(a) Degreasing: commercially available degreasing agent (FINECLEANER (registered trademark) 6400, manufactured by Nihon Parkerizing Co., Ltd.), concentration: 20 g/L, temperature 60° C., immersion: 10 minutes (b) Water rinsing: tap water, normal temperature, immersion: 30 seconds (c) Pickling: hydrochloric acid, concentration: 17.5%, normal temperature, immersion: 10 minutes (d) Water rinsing: tap water, normal temperature, immersion: 30 seconds (e) Chemical conversion coating: commercially available zinc phosphate chemical conversion treatment agent (PALBOND (registered trademark) 3696X, manufactured by Nihon Parkerizing Co., Ltd.), concentration: 75 g/L, temperature: 80° C., immersion: 7 minutes (f) Water rinsing: tap water, normal temperature, immersion: 30 seconds (g) Soap treatment: commercially available reactive soap lubricant (PALUBE (registered trademark) 235, manufactured by Nihon Parkerizing Co., Ltd.), concentration: 70 g/L, temperature: 85° C., immersion: 3 minutes (h) Drying: at 100° C. for 10 minutes (i) Amount of film: 10 g/m²

(2-3) Evaluation Test (2-3-1) Workability (Spike Property) Test

A spike test was performed as a test on the hypothesis of shank reducing when a steel wire is formed into a bolt.

The spike test was performed in accordance with the method defined in JP 05-7969 A. After the test, lubricity was evaluated by a spike height and a forming load. The more the spike height increases and the more the forming load decreases, the more lubricity becomes excellent. As mentioned in the above document, an area expansion ratio in the spike test is about 10 times. Lubricity of the film was evaluated by measuring the load and the spike height during working.

Test piece for evaluation: S45C spheroidizing-annealed material in size of 25 mmφ×30 mm

Evaluation Criteria

Spike performance: spike height (mm)/working load (kNf)×100

The more the value increases, the more spike property becomes satisfactory.

A: Extremely excellent as compared with a phosphate/soap coating film (0.96 or more) B: Excellent as compared with a phosphate/soap coating film (0.94 or more and less than 0.96) C: Equivalent to a phosphate/soap coating film (0.92 or more and less than 0.94) D: Inferior as compared with a phosphate/soap coating film (0.90 or more and less than 0.92) E: Drastically inferior as compared with a phosphate/soap coating film (less than 0.90)

(2-3-2) Workability (Upsetting-Ball Ironing Property) Test

An upsetting-ball ironing test was performed as a test on the hypothesis of forming of a bolt head when a steel wire is formed into a flange bolt. The upsetting-ball ironing test was performed in accordance with the method defined in JP 2013-215773 A. An area expansion ratio in the upsetting-ball ironing test was adjusted to at most 150 or more times, and the area expansion ratio is very large as compared with the above-mentioned spike test. Therefore, it is a test capable of reproducing working that requires high workability for formation of a head part of a hexagon bolt with flange. Seizure resistance of the coating film was evaluated by evaluating the amount of seizure of an ironing surface. Test piece for evaluation: S10C spheroidizing-annealed material in size of 14 mmφ×32 mm

Bearing ball: 10 mmφ SUJ2 Evaluation criteria (Evaluation was performed in accordance with the following criteria A to E based on each seizure state shown in FIG. 1)

Evaluation was made of the area where seizure occurred based on the area of the entire ironing surface.

A: Extremely excellent as compared with a phosphate/soap coating film B: Excellent as compared with a phosphate/soap coating film C: Equivalent to a phosphate/soap coating film D: Inferior as compared with a phosphate/soap coating film E: Drastically inferior as compared with a phosphate/soap coating film

(2-3-3) Film Removability Test

A film removability test was performed as follows. Using an upper mold and a lower mold, each having a plane surface, a columnar test piece was subjected to upsetting at a compression ratio of 50%, and then immersed in an alkali cleaner mentioned below. A film retention ratio was calculated by measuring the weight of a coating film before and after a film removal treatment.

Test piece for evaluation: S45C spheroidizing-annealed material in size of 25 mmφ×30 mm Alkali cleaner: aqueous 2% NaOH solution Film removal conditions: liquid temperature: 60° C., immersion: time: 2 minutes

Treatment Procedure:

Measurement of the weight of a coating film before a film removal treatment, a film removal treatment, water rinsing, drying, and measurement of the weight of a coating film after a film removal treatment were performed in this order.

Film retention ratio (%)=(film weight after film removal treatment/film weight before film removal treatment)×100

Evaluation Criteria:

The more a film retention ratio decreases, the more film removability becomes satisfactory.

A: A film retention ratio is 0% B: A film retention ratio exceeds 0% and less than 8% C: A film retention ratio 8% or more and less than 16% D: A film retention ratio is 16% or more and less than 25% E: A film retention ratio is 25% or more

(2-3-4) Evaluation of Corrosion Resistance (Long-Term Rust Prevention Property)

In summer season, a test piece subjected to the above-mentioned coating film treatment was exposed to an open air atmosphere indoors for two weeks or two months, and then the degree of rusting was observed. It was judged that the more the rust area increases, the more corrosion resistance becomes inferior.

Test piece: SPCC-SD in size of 75 mm×35 mm×0.8 mm Evaluation criteria: A: Extremely excellent as compared with a phosphate/soap coating film (rust area of 3% or less) B: Excellent as compared with a phosphate/soap coating film (rust area of exceeding 3% to 10% or less) C: Identical to a phosphate/soap coating film (rust area of exceeding 10% to 20% or less) D: Inferior to a phosphate/soap coating film (rust area of exceeding 20% to 30% or less) E: Drastically inferior as compared with a phosphate/soap coating film (rust area of exceeding 30%)

The test results are shown in Table 4. As is apparent from Table 4, in Examples, workabilities (spike property, ball ironing property, film removability) and corrosion resistance (long-term rust prevention property) were satisfactory. As a result of subjecting to a zirconium chemical conversion treatment as a surface treatment, higher corrosion resistance was exhibited. In Comparative Examples 14 to 21 in which a ratio of a water-soluble silicate to a water-soluble tungstate deviated from the scope of the present invention, there was a tendency that the results of ball ironing property and corrosion resistance are inferior. In Comparative Examples 22 to 25 in which components other than the silicate and tungstate were included as aqueous inorganic salts, there was a tendency that the results of ball ironing property and corrosion resistance are inferior. In Comparative Example 26 in which the phosphate coating film was subjected to a reactive soap treatment, comparatively excellent performances were exhibited. However, because of containing phosphorus, when subjecting to a heat treatment such as quenching and tempering while having the lubricating coating film on a surface, there is a fear that the steel wire rod becomes fragile as a result of the occurrence of phosphorizing. Therefore, Comparative Example 26 deviates from the object of the present invention. Similarly, Comparative Examples 19 and 22 deviate from the scope of the present invention because of containing phosphorus.

Even if the lubricating coating film contains a water-soluble silicate but contains no water-soluble tungstate, insufficient film removability was exhibited.

TABLE 4 Workability Corrosion resistance Ball (Rust prevention property) Spike ironing Film Two Two Phosphatizing property property removability weeks months property*1 Example 19 A A A A A B Example 20 B B B A B B Example 21 A A A A A B Example 22 C B A A B B Example 23 A A A A A B Example 24 A A A A A B Example 25 A A B A A B Example 26 A B A A A B Example 27 A A A A A B Example 28 A B B A B B Example 29 A A A A A B Example 30 A B A A B B Example 31 B C B A B B Example 32 C A A A A B Example 33 A B A A A B Example 34 A B A A B B Example 35 A B A A A B Example 36 A A A A A B Example 37 A B B A A B Example 38 A B A A A B Comparative Example 14 A D E D D B Comparative Example 15 A D A D D B Comparative Example 16 A D C B D B Comparative Example 17 A D A B D B Comparative Example 18 B D B E E B Comparative Example 19 B D D D D E Comparative Example 20 A D A D D B Comparative Example 21 B D A D D B Comparative Example 22 B D A D D E Comparative Example 23 C D A E E B Comparative Example 24 A D A D D B Comparative Example 25 B E A D D B Comparative Example 26 B B — B B E *1B: There is no possibility of brittle fracture of steel wire rod due to phosphorus because of containing no phosphorus. E: There is possibility of brittle fracture of a steel wire rod due to phosphorus because of containing phosphorus.

As is apparent from the above description, the steel wire rod of the present invention does not exhibit phosphorizing property during a heat treatment because of containing no phosphorus, and also can reconcile high workability and corrosion resistance which are equal to or better than those of the steel wire rod subjected to conventional phosphate and soap treatments. Because of satisfactory film removability of the lubricating coating film due to a cleaner after working, the steel wire rod of the present invention also contributes to an improvement in process efficiency when the subsequent step such as a plating step is performed after forming into a bolt. Therefore, the steel wire rod of the present invention has an industrially high utilization value.

The present invention includes the following aspects.

Aspect 1:

A steel wire rod including a lubricating coating film on a surface, wherein the lubricating coating film contains a water-soluble silicate and a water-soluble tungstate, a mass ratio of water-soluble tungstate/water-soluble silicate being in a range of 0.7 to 10, and contains no phosphorus.

Aspect 2:

A steel wire rod including a lubricating coating film containing no phosphorus, wherein

the lubricating coating film is formed using a composition prepared by mixing a water-soluble silicate and a water-soluble tungstate so as to adjust a mass ratio of water-soluble tungstate/water-soluble silicate in the lubricating coating film in a range of 0.7 to 10.

Aspect 3:

The steel wire rod according to aspect 1 or 2, wherein the lubricating coating film contains a resin, and a mass ratio of resin/(water-soluble silicate+water-soluble tungstate) is in a range of 0.01 to 1.5.

Aspect 4:

The steel wire rod according to aspect 3, wherein the resin is at least one selected from a vinyl resin, an acrylic resin, an epoxy resin, a urethane resin, a phenol resin, a cellulose derivative, a polymaleic acid and a polyester resin.

Aspect 5:

The steel wire rod according to any one of aspects 1 to 4, wherein the lubricating coating film contains a lubricant, and a mass ratio of lubricant/(water-soluble silicate+water-soluble tungstate) is in a range of 0.07 to 1.5.

Aspect 6:

The steel wire rod according to aspect 5, wherein the lubricant is at least one selected from wax, polytetrafluoroethylene, fatty acid soap, fatty acid metal soap, fatty acid amide, molybdenum disulfide, tungsten disulfide, graphite and melamine cyanurate.

Aspect 7:

The steel wire rod according to any one of aspects 1 to 6, wherein the mass of the coating film per unit area of the lubricating coating film is in a range of 1.0 to 20 g/m².

This application claims priority based on Japanese Patent Application No. 2014-070446, filed on Mar. 28, 2014, the disclosure of which is incorporated by reference herein. 

1. A steel wire rod including a lubricating coating film on a surface, wherein the lubricating coating film contains a water-soluble silicate and a water-soluble tungstate, a mass ratio of water-soluble tungstate/water-soluble silicate in the lubricating coating film being in a range of 0.7 to 10, and contains no phosphorus.
 2. A steel wire rod including a lubricating coating film containing no phosphorus, wherein the lubricating coating film is formed using a composition prepared by mixing a water-soluble silicate and a water-soluble tungstate so as to adjust a mass ratio of water-soluble tungstate/water-soluble silicate in the lubricating coating film in a range of 0.7 to
 10. 3. The steel wire rod according to claim 1, wherein the lubricating coating film contains a resin, and a mass ratio of resin/(water-soluble silicate+water-soluble tungstate) is in a range of 0.01 to 1.5.
 4. The steel wire rod according to claim 3, wherein the resin is at least one selected from a vinyl resin, an acrylic resin, an epoxy resin, a urethane resin, a phenol resin, a cellulose derivative, a polymaleic acid and a polyester resin.
 5. The steel wire rod according to claim 1, wherein the lubricating coating film contains a lubricant, and a mass ratio of lubricant/(water-soluble silicate+water-soluble tungstate) is in a range of 0.01 to 1.5.
 6. The steel wire rod according to claim 5, wherein the lubricant is at least one selected from wax, polytetrafluoroethylene, fatty acid soap, fatty acid metal soap, fatty acid amide, molybdenum disulfide, tungsten disulfide, graphite and melamine cyanurate.
 7. The steel wire rod according to claim 1, wherein the mass of the coating film per unit area of the lubricating coating film is in a range of 1.0 to 20 g/m².
 8. The steel wire rod according to claim 2, wherein the lubricating coating film contains a resin, and a mass ratio of resin/(water-soluble silicate+water-soluble tungstate) is in a range of 0.01 to 1.5.
 9. The steel wire rod according to claim 2, wherein the lubricating coating film contains a lubricant, and a mass ratio of lubricant/(water-soluble silicate+water-soluble tungstate) is in a range of 0.01 to 1.5.
 10. The steel wire rod according to claim 2, wherein the mass of the coating film per unit area of the lubricating coating film is in a range of 1.0 to 20 g/m². 